Pixiq

So you're seriously thinking about this lens ... what else might be useful to know? Here are some ideas for extending the effectiveness of this remarkable lens and getting the best out of macro lenses in general (part 1 here)

With the Sigma 150mm f/2.8 EX DG IF HSM on a D300 body and Nikon R1C1 macro speedlight attached I can go 'walk about' several times in any day, especially when I am working on a book, tweaking images for agency submissions and just desperate to get outside … every single day there is something worth photographing—bugs, flowers, moss.

Multipliers

The 150mm f2.8 really scores when used in conjunction with a Sigma x1.4 multiplier, becoming a 210mm f4 macro. This gives x1.4 maximum magnification on the camera sensor, but with the crop-factor of a DX sensor (eg 1.5) you can easily fill the frame with some tiny bugs.

By the way, it is worth noting that on FX you’d need x 2.1 magnification (1.4 x 1.5) on the sensor to do this and fill it to the same extent. In macro work, depth of field decreases with magnification (for a given aperture), and consequently you’d get shallower depth of field at the same aperture with the FX sensor and a subject occupying the same proportion of the viewfinder as on the DX camera. It’s one of those definite advantages of DX (and even smaller) sensor sizes when it comes to macro work—provided you want depth of field rather than shallow focus, that is.

Image quality is barely affected with the x1.4 multiplier attached, and slight softening is only noticeable when you look hyper-critically at images where apertures are smaller than f/18 or so. That is where diffraction starts to become an important element (in brief, light wave fronts spill around the edges of the diaphragm, spread out and create softened images). This is the source of that perennial battle between reducing aperture size to achieve increased depth of field and the wave nature of light where diffraction softens the image.

In practice, a tiny bit of post-production work all but eliminates this softening: I go for smart sharpening or unsharp mask (USM) in Photoshop CS4 or, most often, the combination of ‘sharpen’ and ‘detail’ with the Lightroom 3 sliders and a cut in ‘luminance’ to improve background … simplicity is all.

I have found that judicious use of USM can seemingly compensate for about two stops of ‘degradation’ due to image softening: an empirical judgement—it’s just my visual impression on an A3 print. Sharpness is about personal perception after all: the physical processes involved in diffraction and USM are utterly unconnected.

And, of course, you can also use an 'optimum' aperture where the so-called ‘sweet spot’ lies (usually f/8 or f/ll) and build up incredible depth of field with a composite from a succession of images using Helicon Focus™. I have been working with this for the past year and it is amazing.

In the Field

I often use the multiplier both for shy or small insects: with a Nikon R1C1 macro speedlight at ISO 400 there is sufficient flash power to add a sparkle and to mix with ambient light (more in a future post about lighting set-ups both off-the peg and homemade) and still have a shutter speed of 1/250^th sec. This business of using the small flash heads off-axis is one of the most important elements in creating the impression of sharpness with your precious and expensive macro lens because the angle of the incident light creates tiny shadows that enhance surface details … it is all about fooling the eye.

The combination of 150mm macro, macroflash unit and camera can be hand held but might prove a bit unwieldy for some. Near the ground, I often just use a bean bag for support or the remarkable Novoflex Minipod. which, like everything that comes from the German engineering firm Novoflex, is superbly built—I often rest that on my camera backpack or use it as a chest-pod. Sometimes, a monopod is better than a tripod with insects at eye level and lower … you leave the unit partly extended with one section loose so by pushing down it gets to the height you want, then tighten, tilt forward to frame and focus.

Crop factor—just to clear up a misconception

This seems a useful place to mention 'crop factor' in macro work. It's the primary reason (taking out cost) that I like using a DX camera. It is better for getting frame-filling portraits of smaller subjects in the field. Some writers say that DX cameras ‘magnify’ an image compared to FX (full frame): this is a misleading, not to say inaccurate, statement.

A macro lens that boasts 1:1 or lifesize magnification produces that degree of enlargement on the sensor whatever camera is used with it. The DX camera simply takes a smaller portion of the image which is what you see when you look through the viewfinder. And the depth of field advantage has already been mentioned above.

When you ultimately compare A3 prints from a DX and FX camera used on the same subject with the lens set at 1:1 the image from the DX camera looks electronically ‘magnified’ only because a smaller part of the image has been enlarged to fill the print or computer screen. View the prints on a wall from normal distances (not in front of a screen with Photoshop at 200%) and differences of sharpness wouldn't be discernible for two images taken at ISO 200. An on-screen quality difference between FX and DX becomes apparent to me from ISO 600 up because noise from the smaller sensor sites on a DX camera represents a greater proportion of the output than from the larger ones on some FX sensors.

Whether it's for books, web images or even large prints made with Genuine Fractals—this is an optic that has delivered time and time again.

** You can read Part 1 here